Capillary electrophoresis with capacitively coupled contactless conductivity detection for the determination of urinary ethylmalonic acid for the diagnosis of ethylmalonic aciduria.

Ethylmalonic acid is a metabolic organic acid, and its accumulation in urine is diagnostic of ethylmalonic aciduria. In this study, a simple and fast method employing capillary electrophoresis equipped with capacitively coupled contactless conductivity detection was developed for the detection of ethylmalonic acid in urine samples. The optimized electrophoretic separation was performed in 50 mmol/L 2-(N-morpholino)ethanesulfonic acid solution, buffered at a pH of 6.5, and contained 0.13 mmol/L cetyltrimethylammonium bromide as an electroosmotic modifier. Electrophoresis was run at 28 kV in reversed polarity. The linear range of ethylmalonic acid concentration was between 1 and 100 mg/L with a regression coefficient of 0.9998. This method had good intra- and interday precision with <5% relative standard deviations. The detection limit (signal-to-noise ratio = 3) and the quantification limit (signal-to-noise ratio = 10) values were 0.139 and 0.466 mg/L, respectively. Using our optimized conditions, the method was successfully employed for the detection of ethylmalonic acid in urine sample of ethylmalonic aciduria patient.